<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #fat {
            background-color: red;
            width: 300px;
            height: 1800px;
            position: relative;
            left: 300px;

        }

        #s1 {
            width: 250px;
            /* width: 100%; */
            height: 100px;
            background-color: pink;
            position: absolute;
            /* left: 200px; */
            top: 0px;
            z-index: 1;
        }

        #s2 {
            width: 250px;
            height: 300px;
            background-color: black;
            position: absolute;
            z-index: 999999999;
            opacity: .5;
        }

        #s3 {
            width: 250px;
            height: 200px;
            background-color: yellow;
        }
    </style>
</head>

<body>
    <div id="fat">
        <div id="s1">1</div>
        <div id="s2">2</div>
        <div id="s3">3</div>
    </div>
</body>

</html>